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A male and female brimstone
A male and female brimstone on a hardy plumbago (Ceratostigma willmottianum)

The big afternoon of my gardening year, so far, was sunny, clear and not too hot. The early August tourists were filming our Oxford bushes of blue-flowered hardy plumbago, not the usual one but the earlier and more floriferous Ceratostigma griffithii. In a flurry of French they misidentified them as “sauge bleu”. Out of the bushes flew five, yes five, female brimstone butterflies.

In early July, I described in the Financial Times our strategy for attracting brimstones to our Oxford college. It began last year, was nearly frustrated by a browsing undergraduate and was finally validated, to its professor-coordinator’s relief, by a cache of caterpillars in late June. The bushes we planted to attract them are pale green buckthorns. They are not the evergreen variegated buckthorns which several of you wrote to describe, adding that you had never seen butterflies anywhere near them. The one to plant is Rhamnus cathartica. Fifteen UK nurseries are listed as its stockists in the RHS Plantfinder. It is not much of a looker, as it is green-leaved and, so far, no more than 4ft high. It pulls in the fluttering punters, nonetheless. It draws down brimstones from the sky, hundreds of feet above. Unlike us, they can smell it. Unlike them, I will prune it in late autumn when it loses its leaves.

On a warm Tuesday, there were five brimstones flitting on the plumbago. On Wednesday, there were four. On Thursday, there was a total sighting of six. Has the grand total of our hatch been 15 or were there duplicates or immigrants in the count? I know that most of them are females because I have been reading up on these new admissions to college life. Females are a paler shade of yellow, almost a lemon-white, whereas males are a stronger shade of green-yellow. There may well have been some duplicates in the sightings because brimstones are emphatically not creatures of a day. They are our longest-living British butterflies. They are happy on warm days in the herbaceous border but the females will withdraw to our ivy-mantled walls as soon as the weather turns cold. They will overwinter in this evergreen shelter and will come out again in late spring. Older and slimmer ladies, they will then be courted by males who have checked that the outside world is safe. They will attract up to 10 male suitors and will choose only one. After mating with him, he will give her a big present of food. She will lay eggs for the year’s caterpillars and then die.

Thanks to the brimstones, I am a convert to butterfly gardening. I want orange tips, perhaps a few fritillaries, masses of red admirals and clouds of painted ladies. The apostles of the subject are the late Miriam Rothschild, famous for her scientific studies of fleas, and Clive Farrell, property -king-cum-butterfly-lover, who has done so much to show butterflies at their best. Their book, The Butterfly Gardener, appeared in 1983 and is still well worth reading. It is brief, but very well informed. It has filled me with ideas.

This year has been excellent for some butterflies and less good for others. The winners, I now realise, have been the British residents, the peacocks, tortoiseshells, whites of all kinds and even old friends like walls and commas. The losers have been the migrants, the painted ladies, red admirals and so forth. I have just seen a painted lady on my more common blue plumbago, Ceratostigma willmottianum. It is a sight of wondrous beauty but this year it has a special poignancy. Painted Ladies migrate in great clouds from the north African world, after an Arab spring of their own. They fly all the way to gardens like mine in Britain and return when Britain becomes too chilly. Only recently, have our scientists understood their flight and breeding habits. They fly to Britain and breed here but for years they were thought to do the opposite, flying from Britain to breed in the warmth.

This year, these migrants have come in much smaller numbers. Border controls have had nothing to do with it. The north African winter was probably too dry for them.

A painted lady on a flower of field scabious
A painted lady on a flower of field scabious

How can we help butterflies in September? After reading Rothschild and Farrell I realise I have four assets and need a fifth. I have flowering purple heliotrope, some late-flowering ivy, which I had been considering a weed, plenty of flat-headed sedums and some flowers on buddleias, which I prolong by deadheading. According to Rothschild, heliotropes are a “tremendous attraction”. We gardeners love them for the vanilla scent on their flowers but forget that the leaves contain strong chemicals, the pyrrolizidine alkaloids. They are poisonous to vertebrates but invaluable to butterflies. They suck them up from wilting heliotrope leaves and convert them, I learn, “into a sort of love-dust”. Then they shake it over a female. It “immediately overcomes her natural coyness . . . she is arrested in flight, bewitched . . . copulation ensues”. So far, it has not been found to work for humans and is not available for office use.

I have pots of heliotrope waiting round my house door. Not a butterfly is to be seen on them. What am I doing wrong? Rothschild is so eloquent about butterfly-dating that they cannot have lost their nerve. The way to attract orange tip butterflies is to plant lots of damp-loving Cardamine pratensis, the common old Lady’s Smock. Females fall asleep on it at “about 4.45pm” but are woken up at night and assaulted by “randy males” on the hunt.

No virgin, I learn, is allowed to retire for the night unfertilised. It is even worse than an induction week. “Butterflies,” Rothschild insists, are “ephemeral but brutal creatures, for whom rape is commonplace”. Males will also have sex with other males. There has yet to be a nightclub called the Orange Tip.

On my flat-headed sedums, there are plenty of whites and other butterflies but only on the pale-coloured forms. I now learn that dark-coloured sedums are not nearly so attractive to flying visitors. I prefer them in the garden and will have to adjust the balance. Late-flowering ivy is another matter. Its green-white flowers are heaven for butterflies, though gardeners still pull it out as a weed. I will keep a big curtain where it catches the sun and will use it to persuade a painted lady to stay on until late autumn. Nearby, the best mid-blue buddleia is doing a good job. Buddleia Blue Horizon is a magnet for anything that flutters.

What I need is the coarse Ligularia dentata, still commonly known as clivorum. It is a plant with untidy leaves and heads of yellow flowers but it is heaven on earth for red admirals before they return on their long, mysterious migration. Oddly, butterflies disdain roses. Red admirals even avoid sedums. The ligularia is best in damp soil, so I will smuggle it into the lower garden and watch for its attractive power.

Through butterflies’ eyes, the entire garden seems different. They see so much more yellow than we do. They also see a living where we only see weeds. The subject is limitless and I will keep returning to it. I saw her there, a brimstone in my border and now, I am a believer.

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